Wall following robot

ABSTRACT

An example robot includes a body that is movable relative to a surface, a bumper mounted on the body to enable movement of the bumper relative to the body, a sensor to produce a signal in response to the movement of the bumper relative to the body caused by contact between the bumper and the surface, and a controller to control movement of the body to cause the body to track the surface based on a value. The bumper is movable between an uncompressed position relative to the body and a compressed position relative to the body. The signal varies linearly with the movement of the bumper relative to the body. The value is based on the signal and indicates that the bumper in a partially compressed position has a compression range between the uncompressed position and the compressed position.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of, and claims priorityto, U.S. application Ser. No. 14/682,760, filed on Apr. 9, 2015, theentire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This disclosure relates generally to controlling movement of a robot totrack an obstacle, such as a wall, during movement.

BACKGROUND

Mobile robots may be used to traverse surfaces to perform variousoperations, such as cleaning, vacuuming, or the like. Obstacles, such aswalls, fixtures, or the like, may make it difficult for some mobilerobots to reach some areas. For example, a surface adjacent to theintersection between a wall and a floor may be difficult for a robot totraverse.

SUMMARY

An example robot can maintain contact with a wall surface as the robotexecutes a wall following behavior. A sensor associated with a bumper ofthe robot enables continuous contact between the robot's cleaning padand the wall surface while the robot tracks the wall surface. The sensorcan also detect when the bumper has lost contact with the wall surfaceso that the robot can adjust its own orientation to continue followingthe wall surface.

An example robot includes a body that is movable relative to a surface,a bumper mounted on the body to enable movement of the bumper relativeto the body, a sensor to produce a signal in response to the movement ofthe bumper relative to the body caused by contact between the bumper andthe surface, and a controller to control movement of the body to causethe body to track the surface based on a value. The bumper is movablebetween an uncompressed position relative to the body and a compressedposition relative to the body. The signal varies linearly with themovement of the bumper relative to the body. The value is based on thesignal and indicates that the bumper in a partially compressed positionhas a compression range between the uncompressed position and thecompressed position. The example robot may include one or more of thefollowing features, either alone or in combination.

The surface can include a wall surface. Configurations of the controllerto control movement of the body can include configurations to cause therobot to maintain contact with the wall surface at an angle of betweenabout 3 degrees and about 20 degrees. The robot can include a cleaningpad attached to a bottom of the body and a fluid applicator configuredto dispense fluid from the robot. The cleaning pad can extend beyond thebumper.

Configurations of the controller to control movement of the body tocause the body to track the surface can include configurations to causethe robot to execute a wall following behavior in which the controllercontrols movement of the body to cause the body to contact the wallsurface at an angle such that the bumper is in the partially compressedposition, and in which the controller adjusts rotational andtranslational speeds of the robot to maintain compression of the bumperin the partially compressed position. Configurations of the controllerto control movement of the body to cause the body to track the surfacecan include configurations to cause the robot to maintain contactbetween the cleaning pad and the wall surface in a wall followingbehavior.

The sensor may be a first sensor and the signal may be a first signal.The robot may include a second sensor to produce a second signal inresponse to movement of the bumper. The second signal can vary linearlywith the movement of the bumper. The controller can be programmed tocalculate the value based on a first value that is based on the firstsignal and a second value that is based on the second signal.

The body can have a left side, a right side, a front, and a back. Thefirst sensor can be adjacent to the right side and the second sensor canbe adjacent to the left side. The bumper can be located along the frontof the robot and can extend partially along the left side and the rightside. The robot can include a third sensor to produce a third signal inresponse to movement of the bumper. The third signal can vary linearlywith the movement of the bumper. The third sensor can be between theleft side and the right side, and the third sensor can be adjacent tothe front.

The sensor can be or include a post mounted to the bumper, a magnetmounted to the post, and a Hall Effect sensor mounted in the body abovethe magnet. The sensor can be or include a capacitive sensor. Thecapacitive sensor can include a pair of capacitive plates. At least oneof the capacitive plates can be moveable relative to another of thecapacitive plates based on movement of the bumper. The controller can beprogrammed to determine a time constant from signals produced inresponse to movement of the at least one capacitive plate. The sensorcan be or include an inductive sensor. The inductive sensor can includea core material that is movable within windings based on movement of thebumper. The controller can be programmed to determine a time constantfrom signals in response to movement of the core material.

The surface can include a wall of a room, and the controller can beprogrammed to control movement of the body to track the wall surface tomaintain contact with the wall by maintaining the value within thecompression range. The controller can be programmed to dynamicallycalibrate a position of the bumper relative to the body in response tothe bumper being within a predefined range of the uncompressed position.The controller can be programmed to control movement of the body tocause the body to retreat from the surface in response to the valuebeing outside the compression range and indicative of the bumper beingcompressed further than an amount of compression associated with thecompression range. The controller can be programmed to control movementof the body to cause the body to turn toward the surface in response tothe value being outside the compression range and indicative of thebumper being compressed less than an amount of compression associatedwith the compression range.

The body can include wheels, and the robot can include detectorsassociated with the wheels. The detectors can be for detecting speed ofthe wheels. The controller can be programmed to control movement of thebody to cause the body to retreat from the surface, to turn-away fromthe surface, and then to re-engage the surface based, at least in part,on the speed of the wheels being less than a predetermined speed and thevalue being outside the compression range. The controller can beprogrammed to cause the body to track the surface at an angle. Thecontroller may be programmed to adjust the angle based on the value.

Another example robot can include a body that is movable relative to asurface, a bumper mounted on the body to enable movement of the bumperrelative to the body, linear sensors to produce signals in response tomovement of the bumper relative to the body caused by contact betweenthe bumper and the surface over a period of time, and a controller togenerate one or more control signals based on the signals produced bythe linear sensors. The signals vary linearly with movement of thebumper. The one or more control signals can be for controlling movementof the body to track the surface at least during the period of time. Theexample robot may include one or more of the following features, eitheralone or in combination.

The surface can include a wall surface. Configurations of the controllerto control movement of the body can include configurations to cause therobot to maintain contact with the wall surface at an angle of betweenabout 3 degrees and about 20 degrees. The robot can include a cleaningpad attached to a bottom of the body and a fluid applicator configuredto dispense fluid from the robot. The cleaning pad can extend beyond thebumper.

Configurations of the controller to control movement of the body tocause the body to track the surface can include configurations to causethe robot to execute a wall following behavior in which the controllercontrols movement of the body to cause the body to contact the wallsurface at an angle such that the bumper is in the partially compressedposition, and in which the controller adjusts rotational andtranslational speeds of the robot to maintain compression of the bumperin the partially compressed position. Configurations of the controllerto control movement of the body to cause the body to track the surfacecan include configurations to cause the robot to maintain contactbetween the cleaning pad and the wall surface in a wall followingbehavior.

The linear sensors can include a first linear sensor and a second linearsensor. The first linear sensor can be disposed adjacent to a first sideof the body, and the second linear sensor can be disposed adjacent tosecond side of the body. The linear sensors can include a third linearsensor disposed between the first linear sensor and the second linearsensor.

Each linear sensor can include a post mounted to the bumper, a magnetmounted to the post, and a Hall Effect sensor mounted in the body abovethe magnet. Each linear sensor can be or include a capacitive sensor.The capacitive sensor can include a pair of capacitive plates. At leastone of the capacitive plates can be moveable relative to another of thecapacitive plates based on movement of the bumper. The controller can beprogrammed to determine a time constant from signals produced inresponse to movement of the at least one capacitive plate. Each linearsensor can be or include an inductive sensor. The inductive sensor caninclude a core material that is movable within windings based onmovement of the bumper. The controller can be programmed to determine atime constant from signals in response to movement of the core material.

An example method of controlling a robot includes determining, based onat least one signal that varies linearly with an amount of force betweenthe robot and a surface, that there is a level of contact between therobot and the surface that exceeds a threshold, and controlling therobot to track the surface to maintain at least the level of contactbetween the robot and the surface that exceeds the threshold. Theexample method may include one or more of the following features, eitheralone or in combination.

The threshold can be a lower threshold. The method can includedetermining, based on the at least one signal, that the amount of forcebetween the robot and the surface exceeds an upper threshold, with theupper threshold being greater than the lower threshold, and in responseto determining that the amount of force between the robot and thesurface exceeds the upper threshold, controlling the robot to retreatfrom the surface.

The robot can include wheels. The method can include detecting a speedof the wheels, and based at least in part on the speed of the wheels,controlling the robot to retreat from the surface, to turn-away from thesurface, and then to re-engage the surface.

The determining can be based on two or more signals that vary linearlywith an amount of force between the robot and the surface. The methodcan include controlling an angle at which the robot engages the surfacebased at least in part on the two or more signals.

Advantages of the example robots and methods described herein mayinclude, but are not limited to, the following. In an example, a robotcan clean crevices, corners, and other regions that may be difficult toreach and may accumulate debris. In an example, a robot can clean roomshaving geometries formed by walls and obstacles of the room. In anexample, a robot has a geometry that can cause the robot to misscleaning regions of the room. In such an example, the robot canimplement wall following in order to access regions that other movementand cleaning patterns may miss during the cleaning operation.

Any two or more of the features described in this specification,including in this summary section, can be combined to formimplementations not specifically described herein.

The robots and techniques described herein, or portions thereof, can becontrolled by a computer program product that includes instructions thatare stored on one or more non-transitory machine-readable storage media,and that are executable on one or more processing devices to control(e.g., to coordinate) the operations described herein. The robotsdescribed herein, or portions thereof, can be implemented as all or partof an apparatus or electronic system that can include one or moreprocessing devices and memory to store executable instructions toimplement various operations.

The details of one or more implementations are set forth in theaccompanying drawings and the description herein. Other features andadvantages will be apparent from the description and drawings, and fromthe claims.

DESCRIPTION OF DRAWINGS

FIG. 1A is a perspective view of a mobile robot.

FIG. 1B is a side view of the mobile robot of FIG. 1A.

FIG. 1C is a top view of the mobile robot of FIG. 1A.

FIG. 1D is a top view of a cleaning pad for use with the mobile robot ofFIG. 1A.

FIG. 1E is a top view of a cleaning pad attachment mechanism.

FIG. 1F is an exploded perspective view of the mobile robot of FIG. 1A.

FIG. 1G is a perspective view of a top portion removed from the mobilerobot of FIG. 1A

FIG. 1H is a perspective view of a top portion removed from the mobilerobot of FIG. 1A

FIG. 2A to 2C are top schematic views of a bumper of a mobile robotcontacting a wall surface.

FIG. 3A is a top view of a mobile robot showing the mobile robotscrubbing a floor surface.

FIG. 3B is a top view of a mobile robot executing a cornrow pattern toclean a room.

FIG. 3C is a top view of a mobile cleaning a perimeter of the room ofFIG. 3B.

FIGS. 3D to 3H are top views of an example mobile robot cleaning a roomwith an obstacle.

FIG. 4 is a schematic view of the architecture of a controller of theexample mobile robot of FIG. 1A.

FIGS. 5A to 5F illustrates a mobile robot cleaning an inside corner.

FIGS. 6A to 6E illustrates a mobile robot cleaning an outside corner ofa perimeter.

FIG. 7A to 7D depict an example of a mobile robot cleaning a wallsurface.

FIG. 8 is a flow chart showing a process implemented by a mobile robotto follow a wall surface.

Like reference numerals in different figures indicate like elements.

DETAILED DESCRIPTION

Described herein are example robots configured to traverse surfaces,such as floors, carpets, turf, or other materials. The example robotsmay be configured to perform various operations vis-à-vis the surfacesincluding, but not limited to, vacuuming, wet or dry cleaning, dampcleaning, polishing, and the like.

Open areas of the surfaces may be traversed in a pattern or randomly.Walls or other obstacles (e.g., having vertical surfaces) may affect howthe robot traverses the surface. For example, surfaces adjacent to wallscan be difficult to reach using patterned or random traversal.Accordingly, the example robots described herein employ wall following(also referred to as tracking) techniques that may enable the robots totraverse surfaces adjacent to walls or other obstacles. One exampletracking technique described herein includes using a linear sensor tosense force between the robot and a wall and, in response to the sensedforce, controlling movement of the robot to follow the wall. In someimplementations, the movement of the robot is controlled based onmeasuring the amount of force between the robot and the wall such thatthe measured forced remains within a target range. For example, therobot can contact the wall at an angle (e.g., between 5 and 10 degrees)such that the bumper is partially compressed due to friction between thewall and the bumper. Other implementations are also described.

The example tracking techniques described herein may be used with anyappropriate type of robot or other apparatus that encounters walls orother obstacles in its travels. An example of a robot that employs suchtracking techniques is a mobile robot that can clean a floor surface ofa room by navigating about the room. Referring to FIG. 1A, in someimplementations, a mobile robot 100 navigates and cleans a floor surface10 of a room having a lateral wall surface 20. In some implementations,the robot weighs less than 5 lbs (e.g., less than 2.26 kg) and has acenter of gravity CG. In some implementations, the mobile robot may beautonomous. The robot 100 includes a body 102 supported by wheels (notvisible in FIG. 1A) that can maneuver the robot 100 across the floorsurface 10 based on, for example, a drive command having x, y, and θcomponents. As shown, the robot body 102 has a square shape and definesan X-axis and a Y-axis. The X-axis defines a rightward direction R ofthe robot 100 and a leftward direction L of the robot 100. The Y-axisdefines a rearward direction A (aftward) of the robot 100 and a forwarddirection F of the robot 100. In other implementations, the body 102 canhave other shapes, such as a circular shape, an oval shape, a tear dropshape, a rectangular shape, a combination of a square or rectangularfront and a circular back, or a longitudinally asymmetrical combinationof any of these shapes. The body 102 includes a bottom portion (notshown) and a top portion 108.

Along the bottom portion of the robot body 102, one or more rear cliffsensors (not shown) located in one or both of the two rear corners ofthe robot 100 and one or more forward cliff sensors (not shown) locatedin one or both of the front corners of the mobile robot 100 detectledges or other steep elevation changes of the floor surface 10 andprevent the robot 100 from falling over such floor edges. The cliffsensors may be mechanical drop sensors or light-based proximity sensors,such as an IR (infrared) pair, a dual emitter, single receiver or dualreceiver, single emitter IR light based proximity sensor aimed downwardat a floor surface 10.

The body 102 carries a movable bumper 110 for detecting collisions inlongitudinal (A, F) or lateral (L, R) directions. The bumper 110 ismounted to a front side 102F of the robot body 102 and wraps around tothe right side 102R and a left side 102L of the robot body 102. Thebumper 110 has a shape complementing the robot body 102 and extendsforward of the robot body 102. The bumper 110 includes a lower portion111 extending such that the overall dimension of the front side 102F iswider than a back side 102A of the robot body 102. The robot body 102supports the bumper 110 such that the bumper 110 can translate androtate relative to the robot body 102. As a result, a right portion 110Rand a left portion 110L of the bumper 110 can move in differentdirections. As will be described in more detail herein, a left bumpersensor assembly 112L and a right bumper sensor assembly 112R arepositioned within the robot 100 such that the left bumper sensorassembly 112L can detect movement of the left portion 110L of the bumper110 and the right bumper sensor assembly 112R can detect movement of theright portion 110R of the bumper 110. The right bumper sensor assembly112R is located adjacent to the right side 102R of the robot body 102.The left bumper sensor assembly 112L is located adjacent to the leftside 102L of the robot body 102. In general, the bumper sensorassemblies 112L, 112R can be linear sensor assemblies that provide ananalog signal that is linear with respect to a force on the bumper 110.In some implementations, as described herein, additional sensorassemblies may be included in the robot, e.g., between the left andright sensor assemblies.

In some examples, using a linear sensor that provides an analog sensorcan provide various advantages. For example, the linear sensor providesa signal that varies with the extent of the bumper compression. If thebumper is compressed half-way between an uncompressed position and afully compressed position, the value of the voltage or current from thesensor will be half of the value when the bumper is fully compressed.

Referring to FIG. 1B, the bottom portion of the robot body 102 includesan attached cleaning pad 120. The bottom portion of the robot body 102includes wheels 121 that rotatably support a rearward portion 106 of therobot body 102 as the robot 100 navigates about the floor surface 10.Each of the wheels 121 may be operable with a current sensor 123 thatdetermines the current delivered to each of the wheels 121. Each of thewheels 121 may also be associated with, and operable with, an encoderthat determines a position of each of the wheels 121. The encoder can bean optical encoder that detects the rotational position of the wheel121. Based on the rotational position, a controller of the robot 100 candetermine accelerations and/or speeds of the wheels 121. The cleaningpad 120 supports a forward portion 104 of the robot body 102 as therobot 100 navigates about the floor surface 10. The current sensor 123and the encoder together can sense when the wheels 121 of the robot 100are being driven without movement of the robot in the forward drivedirection F.

A reservoir 122 within the robot body 102 holds a cleaning fluid 124(e.g., cleaning solution, water, and/or detergent). In some examples,the reservoir 122 has a capacity of 170 to 230 mL or about 200 mL. Therobot 100 includes a fluid applicator 126 connected to the reservoir 122by a tube within the robot body 102. In some examples, the fluidapplicator 126 can be a sprayer or spraying mechanism.

The top portion 108 of the robot 100 may include a handle 135 for a userto carry the robot 100. When folded, the handle 135 nests in a recess inthe top portion 108 of the robot 100. The top portion 108 may alsoinclude a toggle button 136 disposed beneath the handle 135 thatactivates a pad release mechanism. The user can also press a cleanbutton 140 to turn on the robot 100 and to instruct the robot 100 tobegin a cleaning operation. The clean button 140 can be used for otherrobot operations as well, such as turning off the robot 100 and/orestablishing a virtual barrier location.

Referring to FIG. 1C, in some cases, the cleaning pad 120 can extendbeyond the width of the bumper 110 such that the robot 100 can positionan outer edge of the pad 120 up to and along tough-to-reach surfaces orinto crevices, such as at a wall-floor interface 30. In some examples,the cleaning pad 120 extends beyond the body 102 of the robot 100 byapproximately 0.1 to 10 mm (e.g., 0.5 mm to 2 mm, 1 mm to 3 mm, 1 mm to5 mm, 2 mm to 5 mm, 3 mm to 6 mm, 5 mm to 10 mm, about 1 mm, about 5 mm,about 10 mm). In such implementations, the ends of the cleaning pad 120contact the wall surface 20 and, as described herein, can cause thebumper 110 to move due to friction forces on the cleaning pad 120. In animplementation, the cleaning pad 120 extends up to the edges and doesnot extend significantly beyond a pad holder (not shown) of the robot.The bumper 110, in this case, contacts the wall surface 20 and moves dueto friction between the bumper and the wall surface 20.

The robot 100 can push the edge of the pad 120 against wall surfaces orother vertically extending surfaces. The position of the cleaning pad120 further allows the cleaning pad 120 to clean the surfaces orcrevices of a wall or other vertically extending surface by the extendededge of the cleaning pad 120 while the robot 100 moves in a wallfollowing motion for a period of time. The extension of the cleaning pad120 can thus enable the robot 100 to clean in cracks and crevices beyondthe reach of the robot body 102. As described herein, as the robot 100initiates a wall following pattern or behavior along a lateral surfaceof the room (e.g., the wall surface 20), the cleaning pad 120 can bepressed against the wall surface 20 so that debris located along thewall-floor interface 30 can be picked up by the cleaning pad 120.

Referring to FIG. 1D, in an example, the cleaning pad 120 includesabsorptive layers 152, an outer wrap layer 154, and a card backing 156.The pad 120 has bluntly cut ends 158 such that the absorptive layers 152are exposed at both ends of the pad 120 and the full length of the pad120 is available for fluid absorption and cleaning. The absorbedcleaning fluid may be securely held by the absorptive layers 152 so thatthe cleaning fluid does not drip from the cleaning pad 120. In somecases, the cleaning pad 120 is disposable. In other cases, the cleaningpad 120 is a reusable (e.g., machine washable) microfiber cloth pad witha durable plastic backing.

Also referring to FIG. 1E, the cleaning pad 120 may be secured to thebottom portion of the robot 100 by a pad holder 160. The pad holder 160may hold the cleaning pad 120 securely in place by grasping the cardbacking 156. The cleaning pad 120 can be installed into the pad holder160 from either of two identical directions (180 degrees opposite to oneanother). The pad holder 160 can release the cleaning pad 120 when a padrelease mechanism 162 is triggered using a toggle button 136 (shown inFIG. 1A).

Referring to FIGS. 1F to 1H, posts 164 traverse the robot body 102 toattach a bumper chassis 171 of the bumper 110 to the robot body 102. Thebumper chassis 171 is fixed to the bumper 110 (e.g., using fasteners).Referring to FIG. 1G, the posts 164 insert into apertures 166 defined bythe robot body 102. The posts 164 may have a cross sectional diametervarying in size along their length and is further sized to fit in theapertures 166 defined by the robot body 102. The posts 164 can be madeof a flexible material (e.g., an elastomer or other resilient material).The material of the posts 164 allows the bumper 110, and hence thebumper chassis 171, to move relative to the robot body 102 upon contactbetween the bumper 110 and an obstacle or vertically oriented orextending surface in the environment.

Referring to FIG. 1H, the robot 100 includes the left sensor assembly112L and the right sensor assembly 112R to detect motion of the bumper110 relative to the robot body 102. In some implementations, additionalsensor assembly(ies) may be included, such as a center sensor assembly(described herein). In some implementations, the left and right sensorassemblies 112L, 112R include linear sensors. In some implementations, alinear sensor has a response to an applied force that is linear over atleast a limited range. In some implementations, the response may belinear over an entire range of the applied force, whereas in otherimplementations, the response may be linear over only a limited range ofapplied force. In other implementations, a non-linear sensor may be usedand the signals from the non-linear sensor can be remapped by, forexample, a controller of the robot to compute an estimate of the appliedforce with respect to the magnitude of the signal. Example linearsensors include Hall Effect sensors, capacitive sensors, or inductivesensors. Any appropriate type of linear sensor may be used. Thefollowing example addresses use of a Hall Effect sensor, which can be atransducer that varies its output voltage in response to a magneticfield. The Hall Effect sensor can operate as an analog transducer,directly returning an analog voltage signal in response to the magneticfield. With a known magnetic field, its distance from the Hall plate canbe determined and the relative position of the magnet can be deducedbased on the measured voltage.

Referring to FIG. 1F, the bumper chassis 171 includes a left pedestal orpost 168L which a left magnet 170L is mounted and housed. The leftmagnet 170L forms part of the left bumper sensor assembly 112L describedabove. The bumper chassis 171 also includes a right post 168R and aright magnet 170R for the right bumper sensor assembly 112R. The magnet170L may be coupled to the post 168L of the bumper chassis 171, whichallows the magnet 170L to move relative to the robot body 102 of therobot 100.

Referring back to FIG. 1H, in this example, a platform 172 is fixed tothe robot body 102. When the bumper 110 moves relative to the robot body102, the bumper chassis 171, which is fixed to the bumper 110, alsomoves relative to the platform 172. The bumper chassis 171 can also beattached to the resilient posts 164 to dampen the dynamic response ofthe bumper 110 (e.g., in response to a force from contact with obstaclesin the environment), dissipate kinetic energy of the bumper, and absorbmechanical shock.

In some implementations, the platform 172 includes a circuit board 174that includes a left Hall Effect sensor 176L and a right Hall Effectsensor 176R. In some implementations, the bumper sensor assemblies 112Land 112R include a first component attached to the robot body 102 (e.g.,sensors 176L, 176R) and a second component attached to the bumper 110via the bumper chassis 171 (e.g., magnets 170L, 170R). Referring back toFIG. 1C, the left bumper sensor assembly 112L includes the left sensor176L coupled to the robot body 102 and the left magnet 170L coupled tothe left portion 110L of the bumper 110 via the bumper chassis 171. Theright bumper sensor assembly 112R includes the right sensor 176R coupledto the robot body 102 and the right magnet 170R coupled to the rightportion 110R of the bumper 110 via the bumper chassis 171. The leftsensor 176L is positioned on or near the left side 102L of the robotbody 102 (shown in FIG. 1A) and above the left magnet 170L. The rightsensor 176R is positioned on or near the right side 102R of the robotbody 102 and above the right magnet 170R. The Hall Effect sensors 176Land 176R generate a voltage in response to nearby magnetic fields, suchas, for example, the magnetic fields generated by the magnets 170L and170R.

The configuration of the left and right bumper sensor assemblies 112Land 112R allow the left and right sensors 176L and 176R to detectmovement of the magnets 170L and 170R relative to the sensors 176L and176R. The magnets 170R, 170L generate magnetic fields that vary instrength at the location of the sensors 176R, 176L as the magnets 170R,170L move farther from or closer to the sensors 176R, 176L. The left andright sensors 176L and 176R, in turn, generate voltages in response tomovements of the left and right magnet 170L and 170R, respectively,relative to the left and right sensors 176L and 176R, respectively. Thevoltages vary linearly with changes in the magnetic field. Thus, thesensors 176L and 176R provide an analog response signal that variesbased on the extent to which the bumper 110 is depressed. As the magnets170L and 170R move farther from their respective sensors 176L and 176R,the strengths of the magnetic fields at the locations of the sensors176L and 176R weaken, and thus the sensors 176L and 176R generate asmaller voltage. In contrast, as the magnets 170L and 170R move closerto their respective sensors 176L and 176R, the strengths of the magneticfields at the locations of the sensors 176L and 176R increase, and thusthe sensors 176L and 176R generate a larger voltage. Since the sensors176L and 176R are coupled to the robot body 102 and the magnets 170L and170R are coupled to the bumper 110, the analog voltages generated by thesensors 176L and 176R correspond to movement of the bumper 110 relativeto the robot body 102 due to, for instance, contact of the bumper 110with obstacles in the room, such as a wall. For example, friction forcebetween the wall and the bumper 110 cause the bumper 110 to move betweenuncompressed and partially compressed positions, causing the Hall Effectsensors to register voltages that vary linearly with the amount ofcompression experienced by the bumper due to friction between the walland the bumper. More specifically, signals from the sensors 176L, 176R(e.g., the voltages of the sensors 176L, 176R) vary linearly with themovement of the bumper 110 relative to the robot body 102.

While the sensors 176L and 176R have been described as Hall Effectsensors, in some implementations, the sensors can be capacitive sensorssuch that the bumper sensor assemblies operate based on a change insensed capacitance by the capacitance sensors. For example, capacitiveplates can replace the magnets 170L and 170R, and a corresponding pairof capacitive plates can replace the Hall Effect sensors 176L, 176R. Thecapacitance of the left and right plate pairs can be measuredindependently using a variety of techniques that, for example,dynamically measure the electric coupling by measuring an RC(resistive-capacitive) time constant. The capacitance of left and rightpairs can vary linearly depending on the distance of the capacitivesensors from the capacitive plates. In other implementations, thesensors 176L, 176R can be inductive sensors. In this case, thecapacitive plates on the circuit board are replaced with spiral PCB(printed circuit board) traces that serve as inductors. The bumperchassis 171 can include core material (instead of the magnets 170L and170R) that passes through the spiral traces. As the bumper 110compresses, an amount of the core material that traverses the spiraltraces can vary, thus causing a change in inductance. The inductance ofthose traces can be measured by measuring the inductive coupling by, forexample, dynamically measuring the LR (inductive-resistive) or LRC(inductive-resistive-capacitive) time constant with an oscillatorcircuit.

While the left and right sensor assemblies 112L and 112R have beendescribed above, in some implementations, the robot may additionallyand/or alternatively include a front sensor assembly located between theleft side of the robot and the right side of the robot. The front sensorassembly can be located adjacent to the front side of the robot and canproduce a signal in response to movement of the bumper in, for example,the right direction R and the left direction L. The front sensorassembly would thus be able to detect forces on the bumper in thelateral direction.

While the magnets 170R, 170L have been described to be fixed to thebumper 110 and the sensors 176R, 176L have been described to be fixed tothe robot body 102, in some implementations, the sensors may be fixed tothe bumper and the magnets may be fixed to the robot body. In suchimplementations, the sensors and magnets can move relative to oneanother to cause the magnetic field at the sensors to vary.

As shown in FIGS. 2A, 2B, and 2C, a neutral position 110N of the bumper110 is shown in dashed lines. The neutral position 110N corresponds tothe position of the bumper 110 before forces are exerted on the bumper110 to cause the bumper 110 to move (e.g., be depressed) relative to therobot body 102. As described in more detail herein, the neutral position110N may vary from one cleaning operation to another cleaning operation.During a cleaning operation, the robot 100 can calibrate the neutralposition 110N such that the neutral position 110N is interpreted as anuncompressed state of the bumper 110. The compression of the bumper 110is herein also interchangeably referred to as rearward translation ofthe bumper 110. The solid lines in FIGS. 2A, 2B, and 2C depicting thebumper 110 correspond to the position of the bumper 110 after a forcecauses the bumper 110 to move relative to the robot body 102.

The bumper 110 can move depending on a direction and position of forceson the bumper 110 (e.g., a relative direction and a relative position ofan obstacle in contact with the bumper 110). Referring to FIG. 2A, whenthe right portion 110R and the left portion 110L move in the rearwarddirection A, the bumper 110 is translating in the rearward direction Arelative to the robot body 102. Contact between a front portion 110F ofthe bumper 110 with an obstacle such as the wall surface 20 as the robot100 moves in the forward direction F can cause the translation of thebumper 110 in the rearward direction A. Referring to FIG. 2B, when therobot 100 encounters an obstacle on the left side of the robot body 102,the bumper 110 is depressed to a greater extent on the left portion 110Lthan the right portion 110R. The left portion 110L moves in the rearwarddirection A while the right portion 110R moves in the forward directionF or in the rearward direction A such that the right portion 110R isdepressed less than the left portion 110L. The bumper 110 translates inthe rearward direction A and rotates counterclockwise relative to therobot body 102 such that, for example, the front of the cleaning pad isangled with respect to the robot body 102. Contact between the leftportion 110L of the bumper 110 with the wall surface 20 as the robot 100moves in the forward direction F can cause the clockwise rotation andrearward translation of the bumper 110 due to, for example, frictionbetween the left portion 110L and the wall surface 20. Referring to FIG.2C, when the robot 100 encounters an obstacle on the right side of therobot body 102, the bumper 110 is depressed to a greater extent on theright portion 110R than the left portion 110L. The right portion 110Rmoves in the rearward direction A while the left portion 110L moves inthe forward direction F or the rearward direction A such that the leftportion 110L is depressed less than the right portion 110R. The bumper110 translates rearward and rotates clockwise relative to the robot body102 such that, for example, the front of the cleaning pad is angled withrespect to the robot body 102. Contact between the right portion 110R ofthe bumper 110 with the wall surface 20 as the robot 100 moves in theforward direction F can cause the clockwise rotation and rearwardtranslation of the bumper 110 due to, for example, friction between theright portion 110R and the wall surface 20. Referring to FIG. 1H, theleft and right bumper sensor assemblies 112L and 112R can detect themovements of the left portion 110L and the right portion 110R describedabove with respect to FIGS. 1A to 1C. In other words, the left and rightbumper sensor assemblies 112L and 112R may be configured to detect thecompression of the left and right portions 110L and 110R of the bumper110.

Although the bumper 110 has been described to contact obstacles, such asvertical surfaces (e.g., walls), in the environment in order to move, insome implementations, the bumper 110 can also move due to contact of thecleaning pad with surfaces in the environment.

The example robots described herein can traverse a surface by followinga pattern, or by traversing it randomly. Example navigational behaviorsof a robot can include a wall following pattern and an area coveragepattern. For example, the wall following pattern can be straight motionpattern, and the area coverage pattern can be a vine pattern, a cornrowpattern, or any combinations of these patterns. Other patterns are alsopossible.

In the straight motion pattern, the robot 100 generally moves in astraight path to follow an obstacle defined by vertical edges, such as awall. The straight motion pattern generally corresponds to wallfollowing behavior. The continuous and repeated use of the birdfootpattern is referred to as the vine pattern or the vining pattern. In thevine pattern, the robot 100 executes repetitions of a birdfoot patternin which the robot 100 moves back and forth while advancingincrementally along a generally forward trajectory. Each repetition ofthe birdfoot pattern advances the robot 100 along a generally forwardtrajectory, and repeated execution of the birdfoot pattern can allow therobot 100 to traverse across the floor surface in the generally forwardtrajectory. In the cornrow pattern, the robot 100 moves back and forthacross a room so that the robot 100 moves perpendicular to thelongitudinal movement of the pattern slightly between each traversal ofthe room to form a series of generally parallel rows that traverse thefloor surface. The robot 100 can execute navigational behaviors thatuses vine and cornrow patterns as the robot 100 traverses the room, anda straight motion pattern as the robot 100 moves about a perimeter ofthe room or edges of objects within the room.

Referring to FIG. 3A, in one example, the robot 100 moves in thebirdfoot pattern mentioned above through a footprint area AF on thefloor surface 10 on which the cleaning fluid 124 has been applied. Thebirdfoot pattern depicted involves moving the robot 100 (i) in a forwarddirection F and a backward or reverse direction A along a centertrajectory 300, (ii) in a forward direction F and a reverse direction Aalong a left trajectory 310, and (iii) in a forward direction F and areverse direction A along a right trajectory 305. The left trajectory310 and the right trajectory 305 are arcuate, extending outward in anarc from a starting point along the center trajectory 300. While theright and left trajectories 305, 310 have been described and shown asarcuate, in other implementations, the left trajectory and the righttrajectory can be straight line trajectories that extend outward in astraight line from the center trajectory.

In the example of FIG. 3A, the robot 100 moves in a forward direction Ffrom Position A along the center trajectory 300. The robot 100 thenmoves in a backward direction A along the center trajectory to adistance equal to or greater than the distance to be covered by fluidapplication. For example, the robot 100 moves backward along the centertrajectory 300 by at least one robot length LR to Position G, which maybe the same position as Position A. The robot 100 applies the cleaningfluid 124 to an area substantially equal to or less than the footprintarea AF of the robot 100. As the robot returns to the wall 20, thecleaning pad 120 passes through the cleaning fluid 124 and cleans thefloor surface 10. From Position B, the robot 100 retracts either along aleft trajectory 310 or a right trajectory 305 to Position F or PositionD, respectively, before going to Position E or Position C, respectively.In some cases, Positions C, E may correspond to Position B. The robot100 can then continue to complete its remaining trajectories. Each timethe robot 100 moves forward and backward along the center trajectory300, left trajectory 310 and right trajectory 305, the cleaning pad 120passes through the applied fluid 124, scrubs dirt, debris and otherparticulate matter from the floor surface 10, and absorbs the dirtyfluid away from the floor surface 10. The scrubbing motion of thecleaning pad 120 combined with the solvent characteristics of thecleaning fluid 124 breaks down and loosens dried stains and dirt. Thecleaning fluid 124 applied by the robot 100 suspends loosened debrissuch that the cleaning pad 120 absorbs the suspended debris and wicks itaway from the floor surface 10.

Referring to FIG. 3B, the robot 100 can navigate about a room 320following a path 325 executing a combination of the vine pattern andcornrow pattern described above to cover the floor surface 10 of theroom. Each row of the cornrow pattern is spaced apart from adjacent rowsby a distance D. In this example, the robot 100 is operating in acleaning mode requiring use of the cleaning fluid 124, so the robot 100is applying the cleaning fluid 124 in bursts ahead of the robot 100along the path 325. The robot 100 advances along the path 325 byperforming the vine pattern, which includes repetitions of the birdfootpattern along each length of the cornrow pattern. With each birdfootpattern, as described herein, the robot 100 ends up at a location thatis generally in a forward direction relative to its initial location.

The path 325 allows the robot 100 to clean a region 326 of the room, butthe vine and cornrow pattern of the path 325 can cause the robot 100 tomiss cleaning a region 327 of the room. The region 327, which can be,for example, a narrow hallway, has a width W. In some cases, the width Wof the region 327 is less than twice a distance D between rows of thecornrow pattern. As a result, when the robot 100 executes the cornrowpattern, the robot 100 may contact the wall 20 without entering theregion 327 and thus may be unable to clean the region 327 simply usingthe cornrow pattern. As described herein, the robot 100, in someimplementations, can detect a doorway 328 or other narrow region havinga width less than about 2 robot widths that separates the region 327from the rest of the room 320 based on a wall following routine.

Wall following behavior allows the robot 100 to clean along a wall/floorinterface (e.g., the wall-floor interface 30 of FIG. 1), clean cornersof the room, and find and clean uncleaned regions adjacent to the wallsurface 20, such as region 327. Referring to FIG. 3C, subsequent to thearea cleaning performed using the cornrow and vine pattern, the robot100 can perform wall following to clean the perimeter of the room. Therobot 100 follows a path 350 as it implements the straight motionpattern by continuously engaging with the wall surface 20 at a slightangle and at a relatively constant force applied to the robot 100. Sincethe robot 100 is operating in a cleaning mode that uses the cleaningfluid 124, the robot applies the cleaning fluid 124 ahead of the robot100 along the path 350. In some examples, contacting the wall surface ata slight angle (e.g., the edge of the robot and the wall are notparallel to one another) can provide the advantage of pressing a portionof the cleaning pad against the wall surface such that the entire floorup to the wall is cleaned by the cleaning pad. In some examples,contacting the wall surface at a slight angle can provide the advantageof enabling the robot to determine that it is positioned against thewall (e.g., with the pad extending to the wall) without causing thecontact and friction between the robot and the wall surface to impedemovement of the robot in the forward direction.

As described herein, the wall following techniques can allow the robot100 to clean areas that may have been missed during the cornrowing andvining behavior along the path 325 of FIG. 3B. In some cases, simplyexecuting cornrowing and vining behavior can cause the robot 100 toneglect cleaning certain regions of the room due to, for example,obstacles, geometric features of the room, and geometric features of therobot 100. As the robot 100 follows the wall surface 20, the robot 100can enter the region 327 of the room 320, and a controller of the robot100 can determine that the robot 100 did not clean the region 327 duringthe cornrow and vine pattern executed earlier. In some cases, uponfinding the region 327, the robot 100 may execute a subsequent cornrowand vine pattern within the region 327. In other cases, the robot 100may execute wall following, and the controller can determine that thewall following about the wall 20 of the region 327 is sufficient toclean the floor surface of the region 327.

Referring to FIG. 3D, in another example, the robot 100 navigates arounda room 372 with an obstacle 375. The robot 100 executes an area cleaningpattern such as the cornrow pattern through the room 372 by following apath 380 to clean a region 382 of the room 372. However, due to contactwith the obstacle 375 (e.g., a toilet), the rows 380 a, 380 b of thepath 380 are shorter than the other rows, and the robot 100 thus doesnot clean a region 384. Thus, a region (e.g., the region 384) behind orobscured by an obstacle (e.g., the obstacle 375) that is accessible bythe robot may remain untraversed during an area cleaning behavior.

After the robot 100 completes the cornrowing and vining path 380,referring to FIG. 3E, the robot 100 executes wall following along theperimeter of the region 384 by, for example, approaching the wall 20 ofthe room 372 and following a path 390. The robot 100 maintains contactwith the wall 20 by maintaining an average bumper extent within aspecified range as it engages the wall 20 to clean along the wall 20 ofthe room 372. The path 390 allows the robot 100 to clean behind theobstacle 375, which the robot 100 previously was unable to reach in thecornrow and vine pattern.

In some cases, the region 384 may be sufficiently large to warrantexecution of a subsequent cornrow and vine pattern in the region 384. Asthe robot 100 cleans along the wall 20, the robot 100 can recognize thatthe boundary defined by the wall 20 may not match a boundary determinedby the controller when the robot 100 executes the cornrow pattern. Therobot 100 then may proceed to find the obstacle 375 and clean around theobstacle 375 by following an obstacle path 391. The robot 100 implementswall following behavior along the lateral surfaces defined by theobstacle 375 such that the robot can clean the interface between theobstacle 375 and the floor surface 10.

Using the cornrow and vining pattern, the robot 100 can fail to enterpassageways that are only slightly larger than the width of the robot(e.g., 1 to 1.2 times larger, 1.2 to 1.4 times larger, 1.4 to 1.6 timeslarger, 1.6 to 1.8 times larger, 1.8 to 2 times larger). In anotherexample, now referring to FIGS. 3F to 3H, the robot 100 cleans anenvironment 392 having a first room 393 and a second room 394 separatedby a doorway 395. The second room 394 is sufficiently large to warrantthe robot 100 to execute a cornrow and vining pattern. As shown in FIG.3F, the robot 100 executes an area coverage pattern 396, e.g., a cornrowand vine pattern, to clean the first room 393. Using the area coveragepattern 396, the robot 100 fails to clean the doorway 395 and the secondroom 394 because, as the robot 100 executes row 396 a of the areacoverage pattern, the robot 100 contacts the wall surface 20 of theenvironment 392 and cannot gain entry into the second room 394 throughthe doorway 395. Each row of the cornrow pattern is spaced apart fromadjacent rows by a distance D_(R), which is approximately the width ofthe robot 100. The doorway 395 has a width W_(D). In some cases, thewidth W_(D) is less than twice the distance D_(R). As shown in FIG. 3G,the robot 100, upon completing the area coverage pattern 396 in thefirst room 393, executes a wall follow pattern 397. The robot 100,following the wall follow pattern 397, is able to travel through thedoorway 395 and gain access to the second room 394. Now referring toFIG. 3H, the second room 394 is sufficiently large that the robot 100can execute an area coverage pattern 398 to clean the second room 394.The robot 100, upon gaining access to the second room 394 using the wallfollow pattern 397 shown in FIG. 3G, executes the area coverage pattern398 to clean the second room 394.

Referring to FIG. 4, an example of a control system 400 of the robot 100includes a controller circuit 405 (herein also referred to as acontroller) that operates a drive 410, a cleaning system 420, a sensorsystem 430 having a bumper sensor system 435, a behavior system 440, anavigation system 450, and a memory 460.

The drive 410 can include wheels (e.g., the wheels 121 shown in FIG. 1B)to maneuver the robot 100 across the floor surface based on a drivecommand having x, y, and θ components. The wheels of the drive 410support the robot body above the floor surface. The controller 405 canfurther operate a navigation system 450 configured to maneuver the robot100 about the floor surface. The navigation system 450 bases itsnavigational commands on the behavior system 440, which can select anavigational pattern or behavior stored in the memory 460. Thenavigation system 450 also communicates with the sensor system 430,using the bump sensor, accelerometers, and other sensors of the robot,to determine and issue drive commands to the drive 410.

The sensor system 430 can additionally include a 3-axis accelerometer, a3-axis gyroscope, and rotary encoders for the wheels (e.g., the wheels121 shown in FIG. 1B). The controller 405 can utilize sensed linearacceleration from the 3-axis accelerometer to estimate the drift in thex and y directions as well and can utilize the 3-axis gyroscope toestimate the drift in the heading or orientation θ of the robot 100. Thecontroller 405 can therefore combine data collected by the rotaryencoders, the accelerometer, and the gyroscope to produce estimates ofthe general pose (e.g., location and orientation) of the robot 100. Insome implementations, the robot 100 can use the encoders, accelerometer,and the gyroscope so that the robot 100 remains on generally parallelrows as the robot 100 implements a cornrow pattern. The gyroscope androtary encoders together can additionally be used by the controller 405to perform dead reckoning algorithms to determine the location of therobot 100 within its environment. The sensor system 430 also includesthe current sensors 123 for the wheels 121 (shown in FIG. 1B). Thecontroller 405 can use the current detected from the current sensor 123to determine the amount of current being deliver to each wheel 121 andthen estimate a speed of the wheel 121.

The controller 405 operates the cleaning system 420 to initiate, forexample, spray commands for a certain duration at a certain frequency.The spray commands can be issued according to the spray schedules storedon the memory 460. The controller 405 can also operate the cleaningsystem 420 to vibrate the cleaning pad 120 to scrub the floor surface10.

The bumper sensor system 435 of the sensor system 430 includes thebumper sensor assemblies 112L and 112R that detect contact of the bumper110 with objects in the environment. The controller 405 can implementthe bumper sensor system 435 by interpreting the voltages produced bythe bumper sensor assemblies 112L and 112R.

Referring back to FIGS. 2A to 2C, using signals from the bumper sensorsystem 435, the controller 405 can determine an extent to which the leftportion 110L of the bumper 110 is compressed (herein also referred to asa left bumper extent), and an extent to the right portion 110R of thebumper 110 is compressed (herein also referred to as a right bumperextent). In other cases, the bumper sensor system 435 can sense thatboth the left portion 110L and the right portion 110R are in a state acompression, which can indicate contact with an obstacle in the forwarddirection F of the robot 100, as shown in FIG. 2A. The left bumperextent and the right bumper extent may each be an amount of compressionbetween the compressed state of the bumper 110 and the uncompressedstate of the bumper 110.

Referring back to FIG. 1H, the position of the magnets 170L and 170Rrelative to the sensors 176L and 176R can be set such that the magnets170L and 170R move relative to the sensors 176L and 176R when the bumper110 is compressed. As a result, the voltage generated by the sensors176L and 176R changes as the bumper 110 is compressed. In particular,the voltage generated by the sensor 176L, 176R increases as the magnet170L, 170R moves closer to the sensor 176L, 176R due to compression ofthe bumper 110, which includes the bumper chassis 171 that houses thesensor 176L, 176R. The left and right bumper extents are thus linearlyproportional to the generated voltages. The controller 405 of the robot100 can normalize the left bumper extent and the right bumper extent asa percentage, and can determine an average bumper extent of the leftbumper extent and the right bumper extent. For each cleaning operation,the controller 405 can also dynamically calibrate the left bumper extentand right bumper extent such that 0% corresponds to the bumper 110 inthe uncompressed state and 100% corresponds to the bumper 110 in thecompressed state. A negative percent may indicate an extension of thebumper 110. As described herein, the control system 400 can utilize thebumper sensor system 435 and the detected left and right bumper extentsto implement wall following behaviors that allow the robot 100 to trackthe surface of a wall or other obstacle (such as a bathroom fixture) andthereby clean hard-to-access corners and crevices defined byintersections of floor surfaces and wall surfaces. For example, whenfollowing a wall, the bumper 110 of the robot 100 will be partiallycompressed due to the friction between the bumper 110 and the wall. Therobot 100 can maintain contact with the wall by maintaining the extentof bumper compression and the difference between the left and the rightbumper compression by continuously adjusting the rotational andtranslational speeds of the robot 100 to maintain nearly constantcompression.

In other cases, the robot 100 can compute a difference between the leftbumper extent and the right bumper extent. A positive differenceindicates that the left bumper extent is greater than the right bumperextent, and a negative difference indicates the right bumper extent isgreater than the left bumper extent. When the robot 100 is performingwall following such that the left portion 110L of the bumper 110 isadjacent the wall surface 20 a, the robot 100 can maintain thedifference to be within a range of, for example, 0% to 10%, 5% to 15%,4% to 20%. When the robot 100 is wall following such that the rightportion 110R of the bumper 110 is adjacent the wall surface 20 a, thecontroller 405 of the robot 100 can maintain the difference to be withina range of, for example, −5% to −15%, −10% to 0%, −20% to −4%, byissuing drive commands to the drive 410. The controller 405 canalternatively determine an average of the left bumper extent and theright bumper extent.

The memory 460 can be loaded with thresholds and limits related to thenormalized average bumper extents, as described herein. The memory 460can also be loaded with a static calibration result performed duringmanufacturing of the robot 100. The static calibration can define arange within which the robot considers dynamic calibration described tobe valid. In some examples, as the robot is used repeatedly, thepositions of the posts holding the bumper will change by a small amount.In order to account for such changes, a calibration process can be usedto determine whether the non-compressed position of the bumper andassociated sensor reading have changed. This calibration can beperformed upon starting up the robot before each cleaning mission and/orcan be performed dynamically every 5-10 seconds during cleaning.

Referring back to FIGS. 1A, 3C, and 4, as the robot 100 follows the wall20 of the room 320, the robot 100 can implement specific processes thatallow the robot 100 to clean the floor surface 10 that closely abuts thewall surface 20. The controller 405 can control movement of the robotbody 102 to cause the body 102 to track the wall surface 20 based on avalue of the average bumper extent. The value is based on the signal orsignals generated by the bumper sensor system 435 (e.g., the bumpersensor assemblies 112L and 112R) and can indicate that the bumper 110 ispartially compressed such that the values are within a compression rangeor interval between the uncompressed state and the compressed state. Thecontroller 405 can then determine whether the bumper 110 is within thecompression range or interval (e.g., based on the normalized bumperextent). For example, the controller 405 may determine that the bumperhas reached a threshold compression level for wall following, e.g., 2%to 2.5%, 2.5% to 3%, 3% to 3.5%, 3.5% to 4%, 4% to 4.5%, 4.5% to 5%, 5%to 5.5%, 5.5% to 6%, 6% to 6.5%, 6.5% to 7%, 7% to 7.5%. Wall followingprocesses may then be executed and continue unabated so long as thebumper remains compressed within a predefined range between thecompressed and uncompressed state (e.g., 2% to 5%, 2.5% to 7.5%, 5% to10%, 5% to 15%, 7.5% to 12.5%, 10% to 15%, 5% to 20%, 10% to 20%). Thatis, the wall-following processes continue so long as the amount of forcebetween the bumper and the robot remains within a specified range. Therobot 100 can maintain the amount of force within the specified range bycontinuously adjusting the rotational and translational speeds of therobot 100 to maintain nearly constant compression of the bumper. If theamount of compression exceeds the upper threshold (e.g., 20%), then thewall following processes may cease, and other processes may take overcontrol of the robot to either reestablish pattern traversal or toreengage a wall or other obstacle to continue wall following, asdescribed herein.

Within the predefined range or interval, the controller 405 of the robot100 can also maintain the average bumper extent and, in some cases, adifference between the left and right bumper extents by continuouslyadjusting its rotational and translational speeds to maintain nearlyconstant compression. While wall following, the robot 100 can travel ata nominal translational speed (e.g., 50 mm/s to 150 mm/s, 150 mm/s to250 mm/s, 250 mm/s to 350 mm/s) while not rotating. When the averagebumper extent deviates from a target average bumper extent stored on thememory 460, the controller 405 can deliver a drive command to the drive410 to reduce the speed of the robot 100 an amount proportional to thedeviation. When the bumper extent difference deviates from a targetdifference stored on the memory 460, the controller 405 can deliver adrive command to the drive 410 to increase the rotational velocity ofthe robot 100 an amount proportional to the deviation. In someimplementations, the rotational and translational speeds can be adjustedan amount proportional to the rate of change of the average bump extentand the bump extent difference, respectively.

In some cases the uncompressed position may vary from one cleaningoperation to another cleaning operation due to positional variations inthe resilient posts 164 (shown in FIG. 1F) that mount the bumper 110 tothe robot body 102. During a cleaning operation, the controller 405 candynamically calibrate the uncompressed position to account for thevariations in a position of the bumper 110 relative to the robot body102. The controller 405 can calibrate an initial position of the bumper(when the bumper is not contacting a wall surface) relative to theresilient posts 164 at the start of the cleaning operation. For example,the voltage signals of the bumper sensor assemblies 112L and 112R whilethe bumper is in the neutral position can be set to correspond to theuncompressed position. In other words, those voltage signals canindicate a normalized average bumper extent of 0%. As described above,the memory 460 may include a range of valid voltages (and thus a rangeof valid calibrations) that can generally indicate a normalized averagebumper extent of 0%.

FIGS. 5A to 5F show an example of behavior that the robot 100 canimplement to clean along the wall 20 of a room. In this example, thewall surface 20 includes an inside corner 500, which is defined by theintersection of a wall surface 20 a and a wall surface 20 b.

Referring to FIG. 5A, the robot 100 approaches the inside corner 500executing a wall following behavior. During the wall following behavior,the robot 100 places the cleaning pad against the wall surface 20 a sothat the cleaning pad can clean the interface between the wall 20 andthe floor surface 10 (e.g., the wall-floor interface 30 of FIG. 1). Therobot 100 can achieve such proximity with the wall surface 20 bycontacting the wall surface 20 a with the bumper 110 of the robot 100.Contact is at a slight angle (e.g., between about 1 degree and about 10degrees, between about 3 degrees and about 15 degrees, between about 3degrees and about 20 degrees, between about 5 degrees and about 20degrees, between about 3 degrees and about 10 degrees, between about 10degrees and about 20 degrees) so as to maintain sufficient contact forcebetween the wall 20 and the bumper 110 and to continue wall followingfor at least as long as the force is maintained. In this example, therobot 100 contacts the wall surface 20 a with the right portion 110R ofthe bumper 110 so that the cleaning pad can follow the wall-floorinterface (e.g., the wall-floor interface 30 of FIG. 1). Contactsufficient for wall following is detected when the amount of forcebetween the bumper and the wall is within a desired range of compressionwith the bumper 110 partially compressed.

During wall following, the robot 100 can position itself against thewall so as to maintain the bumper 110 in a partially compressed statesuch that the average bumper extent is within a predetermined interval(e.g., the compression range or interval), which can be, for example, 0%to 5%, 2.5% to 7.5%, 5% to 10%, 5% to 15%, 5% to 20%, 7.5% to 10%, 7.5%to 12.5%, 10% to 15%, 10% to 20%. In some examples, above this interval,the robot 100 may press the bumper 110 against the wall surface 20 awith too much force, which can impede the forward movement of the robot100 and/or indicative of an obstacle. Below this interval, the robot 100may not press the bumper 110 sufficiently hard against the wall surface20 b to allow the cleaning pad 120 to reach the crevices and cornersdefined by the floor surface 10 and the wall surface 20 a. If thecontroller 405 detects force above the foregoing interval, thecontroller 405 may initiate operations to move the robot away from thewall, and either reengage with the wall (for further wall following) ordisengage with the wall. If the controller 405 detects force below theforegoing interval, the controller may initiate operations to move therobot in further contact with the wall or commence a coverage pattern,such as the cornrow and vine pattern.

Referring to FIG. 5B, in this example, the robot 100 follows the wallsurface 20 a until it contacts the wall surface 20 b with the frontportion 110F of the bumper 110. Upon contacting the wall surface 20 bwith the front portion 110F, the average bumper extent increases beyondan upper threshold bumper extent for wall following, indicating that therobot 100 is pushing against a surface (e.g., the wall surface 20 b)with the front portion 110F of the bumper 110. The upper threshold ofthe normalized average bumper extent can be, for example, 7% to 8%, 7.5%to 8%, 8% to 9%, 9% to 10%, 10% to 11%, 11% to 12%, 12 to 13%, 13% to14%, 14% to 15%, 15% to 16%, 16% to 17%, 17% to 18%, 18% to 19%, 19% to20%. In some cases, based on signals from the current sensors 123 and/orthe encoders, the controller 405 can determine that the wheels of therobot 100 are moving slower than a predetermined speed, thus indicatingthe robot 100 is no longer advancing along the wall surface 20 a. Aforce on the bumper 110 of the robot 100 can be estimated based on thespeed of the wheels as compared to the current delivered to the wheels.The speed of a wheel divided by the current delivered to the wheel isproportional to the force on the wheel, so the controller 405 cancompute a force on each wheel. The controller 405 can determine thespeed of the wheels based on signals from encoders operable with thewheels and the current of the wheels based on signals from the currentsensors 123 of the wheels. The controller 405 can then estimate theforce on each wheel, compute the difference between the estimatedforces, and compute the torque about a center of mass of the robot basedon the difference. The controller 405 can compute a force on the bumper110 based on the torque. In some implementations, the memory 460 caninclude a target force range (e.g., 0.1 N to 0.2 N, 0.1 N to 0.3 N, 0.1N to 0.5 N, 0.5 N to 1 N) that the controller 405 can maintain while thebumper 110 contacts vertically oriented surfaces.

In FIGS. 5C, 5D, and 5E, the robot 100 seeks to re-engage wall followingbehavior along the wall surface 20 b (e.g., on the other wall of thecorner). Referring to FIG. 5C, when the average bumper extent exceedsthe threshold bumper extent, the robot 100 can respond by stoppingforward movement and reverse driving the robot 100 such that the robot100 backs away from the wall surface 20 b so that the bumper 110 nolonger is in a compressed state. The robot 100 can continue backing upuntil the average bumper extent decreases below a lower threshold of thebumper extent, which can be, for example, 7.5% to 7%, 7% to 6%, 6% to5%, 5% to 4%, 4% to 3%, 3% to 2%, 2% to 1%, 1% to 0%, less than 0%. Oncethe average bumper extent decreases below the lower threshold, the robot100 can continue backing up so that the bumper 110 is a predeterminedbacking up distance BD from the wall surface 20 b. The distance BD canbe selected such that the robot 100 has sufficient space to turn aroundand begin wall following along the wall surface 20 b. In some cases, thedistance BD can be, for example, 5 mm to 10 mm, 10 mm to 15 mm, 15 mm to20 mm, 20 mm to 25 mm, 25 mm to 30 mm, 30 mm to 35 mm, about 10 mm,about 20 mm, about 30 mm. The controller 405 can estimate the distanceof the bumper 110 from the wall surface 20 b by using signals outputtedby the accelerometer and/or wheel encoders of the sensor system 430 andcan compare the estimated distance to the distance BD.

Referring to FIG. 5D, in this example, the robot 100 turns away from thewall surface 20 a so that the robot 100 can orient its forward drivedirection F in a direction substantially parallel with the wall surface20 b (e.g., perpendicular to the prior direction of travel in cases of a90-degree corner. Referring to FIG. 5E, the robot 100 then re-engageswall following behavior with the wall surface 20 b. At this point, therobot 100 can continue to engage the right portion 110R of the bumper110 with the wall surface 20 b until the average bumper extent is withinthe predetermined interval described herein. After the robot 100 hasre-engaged the wall following behavior, now referring to FIG. 5F, therobot 100 continues to execute wall following behavior along the wallsurface 20 b by maintaining force against the wall so that the averagebumper extent remains within the predetermined interval. The robot 100can cause the bumper extent to increase by maintaining contact of theright portion 110R of the bumper 110 with the wall surface 20 b.

FIGS. 6A to 6E illustrate an example of behavior that the robot 100 canimplement to clean the wall 20 including an outside corner 600, which isdefined by the intersection of a wall surface 20 c and a wall surface 20d.

Referring to FIG. 6A, the robot 100 approaches the outside corner 600executing a wall following behavior. During the wall following behavior,the robot 100 places the cleaning pad closely against the wall surface20 c so that the cleaning pad can clean the interface between the floorsurface 10 and the wall 20 (e.g., the wall-floor interface 30 of FIG.1). The robot 100 can achieve such proximity with the wall surface 20 bycontacting the wall surface 20 c with the bumper 110 of the robot 100,either tangentially or at a slight angle (e.g., between about 1 degreeand about 10 degrees, between about 3 degrees and about 15 degrees,between about 3 degrees and about 20 degrees, between about 5 degreesand about 20 degrees, between about 3 degrees and about 10 degrees,between about 10 degrees and about 20 degrees) between the wall surface20 and the bumper 110. For example, the robot 100 contacts the wallsurface 20 c with the right portion 110R of the bumper 110 so that thecleaning pad can follow the wall-floor interface. During wall following,the robot 100 can maintain the bumper 110 compression such that theaverage bumper extent is within the predetermined interval describedherein. Above this interval, the robot 100 may be pressing the bumper110 against the wall surface 20 c with too much force, which can impedethe forward movement of the robot 100. Below this interval, the robot100 may not be pressing the bumper 110 sufficiently hard against thewall surface 20 d to allow the cleaning pad 120 to reach the crevicesand corners defined by the floor surface 10 and the wall surface 20 c.In some implementations, smaller force thresholds can increase therelative effect of noise, making it more likely that the robot 100 failsto closely follow corners.

Referring to FIG. 6B, in an example implementation, the robot 100follows the wall surface 20 c until it detects that the average bumperextent is no longer within the predetermined interval. In particular,the robot 100 can detect that the bumper 110 has lost contact with thewall surface 20 c and that the average bumper extent is below a lowerthreshold bumper extent (e.g., the bumper 110 is no longer partiallydepressed). When the right portion 110R of the bumper 110 loses contactwith the wall surface 20 c, in this example, the average bumper extentdecreases below the lower threshold bumper extent because the frictionforce between the wall surface 20 c and the right portion 110R no longercompresses the bumper 110. The decrease in the average bumper extentindicates that the robot 100 is no longer wall following. The lowerthreshold of the bumper extent can be, for example, 7.5% to 7%, 7% to6%, 6% to 5%, 5% to 4%, 4% to 3%, 34% to 2%, 2% to 1%, 1% to 0%, lessthan 0%. Upon detection that the bumper 110 has lost contact, the robot100 can cease forward movement.

In FIGS. 6C and 6D, the robot 100 seeks to re-engage wall followingbehavior along the wall surface 20 d. Referring to FIGS. 6C and 6D, whenthe average bumper extent is below the lower threshold bumper extent,the robot 100 can respond by turning toward the direction of theoriginally followed wall 20 c and slowly advancing the robot 100 untilthe right portion 110R of the bumper 110 engages with the wall surface20 d. In some implementations, upon determining that the average bumperis below the lower threshold bumper extent, the controller 405 of therobot 100 can issue a drive command to the drive 410 to cause the wheelsof the robot 100 to reverse direction so as to move the robot 100 in therearward direction A. After the controller 405 determines that the robot100 has moved the predetermined distance in the rearward direction Abased on, for example, signals from encoders of the wheels, thecontroller issues a drive command to the drive 410 that causes thewheels of the robot 100 to turn the robot 100 so that the forward drivedirection F is substantially parallel to the wall surface 20 d. In somecases, the drive command causes the wheels to turn the robot 100 so thatthe forward drive direction F forms the slight angle (e.g., betweenabout 1 degree and about 10 degrees, between about 3 degrees and about15 degrees, between about 3 degrees and about 20 degrees, between about5 degrees and about 20 degrees, between about 3 degrees and about 10degrees, between about 10 degrees and about 20 degrees) with the wallsurface 20 d.

After the robot 100 has re-engaged the wall following behavior with thewall surface 20 d, now referring to FIG. 6E, the robot 100 continues toexecute wall following behavior along the wall surface 20 b bymaintaining the average bumper extent within the predetermined interval.

Referring back to FIG. 3B, in some implementations, the robot can detecta doorway 328 by engaging with the wall surface 20 at points 325 a and325 b that flank the doorway 328. At the points 325 a and 325 b, therobot 100 contacts the wall surface 20 such that about only half of thefront of the bumper is in contact with the wall surface 20. In somecases, about 25% to 75%, 40% to 60%, 45% to 55% of the front of thebumper is in contact with the wall surface 20. At the point 325 a, thecontroller 405 of the robot 100 can, based on the bumper extent detectedby the left bumper sensor assembly 112L and the bumper extent detectedby the right bumper sensor assembly 112R, determine that the rightportion 110R of the bumper 110 has engaged with the wall surface 20 andthe left portion 110L of the bumper 110 has not engaged with the wallsurface 20. The controller 405 can thus determine that the wall surface20 may not continue from where the right portion 110R contacts the wallsurface 20 to where the left portion 110L is positioned. At the point325 b, the controller 405 can determine that the left portion 110L ofthe bumper 110 has engaged with the wall surface 20 and the rightportion 110R of the bumper 110 has not engaged with the wall surface 20.The controller 405 can thus determine that the wall surface 20 may notcontinue from where the left portion 110L contacts the wall surface 20to where the right portion 110R is positioned. Based on the contact withthe bumper 110 at points 325 a, 325 b, the controller 405 can determinethat an opening—such as the doorway 328—exists between the points 325 a,325 b. The controller 405 can compute a distance between the point 325a, 325 b—which is approximately 2D—and determine that the 328 has awidth W less than 2D.

As shown in FIGS. 5A, 5F, 6A, and 6E, the robot 100 follows wallsurfaces 20 a and 20 b by maintaining contact between the right portion110R of the bumper 110 with the wall surfaces 20 a and 20 b. In someimplementations, the robot 100 can additionally and/or alternativelyfollow wall surfaces or vertically oriented surface by maintainingcontact between the left portion 110L of the bumper 110 with the wallsurfaces. The contact generates a friction that causes compression ofthe bumper 110, which the robot seeks to maintain within thepredetermined interval in some implementations. In some implementations,the cleaning pad 120 may extend beyond the bumper 110, and the cleaningpad 120 and the bumper 110 can be configured such that forces exerted onthe cleaning pad 120 transfer to the bumper 110. For example, referringto FIG. 1G, the resilient posts 164 can mechanically connect thecleaning pad 120 with the bumper 110. As a result, friction forces onthe cleaning pad 120 can compress the bumper and thus increase theaverage bumper extent.

Referring to FIGS. 7A to 7D, the robot 100 can maintain contact betweenthe cleaning pad 120 and the wall surfaces 20 a and 20 b whilemaintaining contact between the bumper 110 and the wall surfaces 20 a,20 b, 20 c, and 20 d by following the wall surfaces such that theforward drive direction F and the wall surfaces 20 a, 20 b, 20 c, and 20d form a slight angle θ (e.g., between about 1 degree and about 10degrees, between about 3 degrees and about 15 degrees, between about 3degrees and about 20 degrees, between about 5 degrees and about 20degrees, between about 3 degrees and about 10 degrees, between about 10degrees and about 20 degrees). The predetermined interval can be withina similar interval as the interval described with respect to FIGS. 5A,5F, 6A, and 6E (e.g., 0% to 5%, 2.5% to 7.5%, 5% to 10%, 5% to 15%, 5%to 20%, 7.5% to 10%, 7.5% to 12.5%, 10% to 15%, 10% to 20%). In somecases, the predetermined interval may be greater than the predeterminedinterval used in the cases described with respect to FIGS. 5A, 5F, 6A,and 6E so that the amount of friction is sufficient between the cleaningpad 120 and the wall surface. For example, the interval can be greaterby, for example, 0% to 1%, 1% to 2%, 2% to 3%, 3% to 4%, 4% to 5%, about1%, about 2%, about 3%. To sufficiently compress the cleaning pad 120,the robot 100 can orient itself so that the forward drive direction F ofthe robot 100 forms the slight angle θ with the wall surfaces 20 a, 20b, 20 c, and 20 d. The angle θ allows a part of the forward drivedirection F to push the cleaning pad 120 into the wall surfaces 20 a, 20b, 20 c, and 20 d, thus generating greater compressive forces on thecleaning pad 120 and greater frictional forces on the bumper 110.

Referring to FIG. 8, a flow chart 800 illustrates an example method ofimplementing a wall following behavior.

At operation 805, a controller of a robot outputs a control signal tothe robot to follow a wall surface. The controller may output thecontrol signal after detecting that the robot has completed cornrow andvine behavior. The robot may be following a wall surface having a firstsurface portion and a second surface portion. The first and secondsurface portions may define a corner, as is described with respect toFIGS. 5A to 5F and 6A to 6E. In some implementations, the controller isprogrammed to dynamically calibrate a position of the bumper relative tothe robot body. The calibration occurs prior to wall following when therobot is not expected to be in contact with a vertically orientedsurface or obstacle that causes the bumper of the robot to becompressed. If the measured position is not within a predefined range,the controller of the robot can issue a drive command that causes therobot to move to an open area to ensure that the bumper of the robot isnot contacting an obstacle. The controller can also issue a drivecommand to stop movement of the robot to avoid inadvertent forces on thebumper. The predefined range can be a static calibration performedduring manufacturing, as described above. The dynamic calibration canoccur before the controller outputs a control signal to follow the wallsurface.

At operation 810, the controller receives a signal from a linear sensoron the robot. The robot can be implementing wall following such that abumper of the robot is contacting a first wall surface. The sensor canbe, for example, the bumper sensor assembly 112R, 112L as describedherein. The signal can be voltage, current, frequency, or otherelectrical signal. The sensor produces a variable signal in response tomovement of a bumper relative to a body of the robot. The signal changesin response to contact between the bumper and the wall surface, and thesignal can vary linearly with the movement of the bumper relative to thebody. The controller can receive two or more signals from two or moresensors on the robot. A first sensor can produce a first signal inresponse to movement of the bumper, and a second sensor can produce asecond signal in response to movement of the bumper. The first andsecond signals can vary linearly with the movement of the bumper. Insome examples, the bumper position is determined based on an average ofthe two linear sensor values.

At operation 815, the controller determines a value X indicative ofcompression of a bumper on the robot. The value X can be, for example, abumper extent. The controller can control the movement of the body ofthe robot based on the determine value X. The controller can cause thebody to track or follow the wall surface based on the value X. In caseswhere the robot has more than one sensor to detect movement of thebumper, the controller can calculate the value X based on separatevalues from each of the sensors. The value X can be based on the signalfrom the linear sensor, and the controller can determine whether thebumper is within a compression range between an uncompressed positionand a partially compressed position based on the value X. When thecontroller determines the value X based on two or more signals that varylinearly with an amount of force between the robot and the wall surface,the value X is additionally or alternatively indicative of an angle atwhich the robot engages the surface. The angle can be based on two ormore sensor signals that are indicative of the value X. The controllercan control the angle at which the robot engages the wall surface basedon the value X. In some implementations, the controller can control anamount of force with which the robot engages the wall surface.

If the value X is above a lower limit LL and below an upper limit UL ofa compression range, at operation 820, the controller outputs a controlsignal to follow the wall surface by issuing a drive signal to cause therobot to continue in the forward drive direction. The control signal maybe the same as the control signal outputted at operation 805. In somecases, the control signal may adjust a drive of the robot in order tomaintain the value X within an optimal value. In some cases, the value Xcan be based on the signal from the sensor and can indicate that thebumper is within the compression range between the uncompressed positionand the compressed position. If the value X is the average normalizedbumper extent, the lower limit LL of the compression range may be, forexample, 7.5% to 7%, 7% to 6%, 6% to 5%, 5% to 4%, 4% to 3%, 34% to 2%,2% to 1%, 1% to 0%, less than 0%. The upper limit of the compressionrange may be, for example, 7% to 8%, 7.5% to 8%, 8% to 9%, 9% to 10%,10% to 11%, 11% to 12%, 12 to 13%, 13% to 14%, 14% to 15%, 15% to 16%,16% to 17%, 17% to 18%, 18% to 19%, 19% to 20%. The optimal value may bethe average of the lower limit LL and the upper limit UL. In someimplementations, the lower limit LL can be between approximately 0% and7.5% or less, and the upper limit can be between approximately 7.5% and15% or more. Keeping the average bumper extent within this predeterminedinterval or compression range can be beneficial in maintaining themobility of the robot while facilitating cleaning of corners andcrevices defined by the first wall surface. The control signal can causethe robot to follow the wall surface that the robot followed atoperation 805 by maintaining the value X within the predeterminedinterval or compression range. The controller can be programmed tocontrol movement of the robot body to track the wall surface to maintainthe value X within the compression range.

If the value X is below the lower limit LL or above the upper limit ULof the compression range, at operation 825, the controller outputs acontrol signal to re-engage the wall surface. The controller can beprogrammed to control movement of the robot body to cause the robot bodyto retreat from the wall surface in response to the value being outsidethe compression range. In some implementations, the controller canreceive a signal from a sensor that detects a speed of the wheels. Thesensor can be, for example, encoders or current sensors operable withwheel. Based on, for example, the speed of the wheels and the bumpersensors, the controller can control the robot to retreat from the wallsurface, to turn-away from the wall surface, and then to re-engage thewall surface. In cases when the value X is above the upper limit UL, thecontroller can implement the re-engagement behavior as described withrespect to FIGS. 5B to 5E above. For example, the controller can delivera control signal to cause the robot to stop forward movement momentarilyand then retreat away from the wall surface. The control signal can alsocause the robot to turn-away from the wall surface, and then re-engagewith the wall surface. In cases when the value X is below the lowerlimit LL, which can indicate a loss of contact between the bumper andthe wall surface, the controller can implement the re-engagementbehavior as described with respect to FIG. 6B to 6D above. Thecontroller can deliver a control signal to cause the robot to stopforward movement momentarily and, in some implementations, cause therobot to retreat toward the wall surface. The control signal can thencause the robot to turn toward the wall surface and then re-engage withthe wall surface.

While the magnets 170L and 170R and the sensors 176L and 176R have beendescribed to be positioned such that compression of the bumper 110results in an increase in the voltage generated by the sensors 176L and176R, in other implementations, the magnets and the sensors can bepositioned such that the magnets are farther from the sensors as thebumper is compressed. In such implementations, the sensors generate asmaller voltage upon compression of the bumper.

While the navigational behaviors described above have been explainedwith respect to the robot 100 executing wet cleaning, in some cases, therobot 100 may execute dry cleaning and may not incorporate all of theabove described navigational behaviors—or may incorporate additionalbehaviors—in a cleaning operation. For example, the robot 100 mayexecute the cornrow pattern without the vine pattern.

In some examples, the robot knows the location of a surface that is haspreviously traversed by storing those locations on a map stored on thenon-transitory-memory 460 of the robot or on an external storage mediumaccessible by the robot through wired or wireless media during acleaning run. In some implementations, the robot includes anupward-facing camera and/or one or more ranging lasers for building sucha map of a space. In some examples, the controller 405 uses a map ofwalls, furniture, flooring changes and other obstacles to position andpose the robot at locations far enough away from obstacles and/orflooring changes prior to the application of cleaning fluid.

While a bumper has been described to detect the amount of force on therobot, in some implementations, a force sensor, a pressure sensor, orsome other sensor disposed on the robot can be used to sense the force.The example wall following techniques described herein can be controlledor implemented, at least in part, using one or more computer programproducts, e.g., one or more computer programs tangibly embodied in oneor more information carriers, such as one or more non-transitorymachine-readable storage media, for execution by, or to control theoperation of, one or more data processing apparatus, e.g., aprogrammable processor, a computer, multiple computers, and/orprogrammable logic components.

While in some examples described above, the wall following behavior isused to clean a perimeter of a room or other space subsequent tocompletion of an area cleaning behavior, in other examples, the wallfollowing behavior can be used to allow the robot to escape from acluttered environment or a bounded area. For example, if the robotenters a space with a narrow opening for entry/exit, the robot maybecome stuck within the space and normal coverage patterns may not alignwith the entry/exit to allow the robot to escape. In such situations,the robot can determine that it is in a cluttered environment andexecute a wall following behavior to escape from the area. Following thewall allows the robot to identify a narrow exit that the robot mightotherwise have difficulty locating. In one particular example, a robotcan execute a random traversal cleaning pattern and upon identifyingthat the robot has repeatedly traversed the same area (e.g., is trappedin a small space or cluttered area) the robot can execute a wallfollowing behavior to exit or escape the area.

A computer program can be written in any form of programming language,including compiled or interpreted languages, and it can be deployed inany form, including as a stand-alone program or as a module, component,subroutine, or other unit suitable for use in a computing environment.

Operations associated with implementing all or part of the wallfollowing techniques described herein can be performed by one or moreprogrammable processors executing one or more computer programs toperform the functions described herein. Control over all or part of thewall following techniques described herein can be implemented usingspecial purpose logic circuitry, e.g., an FPGA (field programmable gatearray) and/or an ASIC (application-specific integrated circuit).

Processors suitable for the execution of a computer program include, byway of example, both general and special purpose microprocessors, andany one or more processors of any kind of digital computer. Generally, aprocessor will receive instructions and data from a read-only storagearea or a random access storage area or both. Elements of a computerinclude one or more processors for executing instructions and one ormore storage area devices for storing instructions and data. Generally,a computer will also include, or be operatively coupled to receive datafrom, or transfer data to, or both, one or more machine-readable storagemedia, such as mass PCBs for storing data, e.g., magnetic,magneto-optical disks, or optical disks. Machine-readable storage mediasuitable for embodying computer program instructions and data includeall forms of non-volatile storage area, including by way of example,semiconductor storage area devices, e.g., EPROM, EEPROM, and flashstorage area devices; magnetic disks, e.g., internal hard disks orremovable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks.

Elements of different implementations described herein may be combinedto form other embodiments not specifically set forth above. Elements maybe left out of the structures described herein without adverselyaffecting their operation. Furthermore, various separate elements may becombined into one or more individual elements to perform the functionsdescribed herein.

What is claimed is:
 1. A mobile cleaning robot comprising: a drivesystem to move the robot across a floor surface and relative to a wallsurface; a bumper movable between a fully uncompressed position and afully compressed position; a pad holder on a bottom portion of therobot; the pad holder configured to receive a cleaning pad extendingbeyond right and left sides of the robot and facing the floor surface;and a controller configured to advance the robot, in a wall followingbehavior, along the wall surface while maintaining contact between aportion of the cleaning pad and the wall surface, while maintaining aposition of the bumper within a range between the fully uncompressedposition and the fully compressed position, and while maintaining anon-zero angle between the right side or the left side of the robot andthe wall surface.
 2. The robot of claim 1, wherein configurations of thecontroller to advance the robot along the wall surface compriseconfigurations to adjust rotational and translational speeds of therobot to maintain the contact between the portion of the cleaning padand the wall surface.
 3. The robot of claim 1, wherein the non-zeroangle between the right side or the left side of the robot and the wallsurface is between about 1 degree and about 20 degrees.
 4. The robot ofclaim 1, wherein the non-zero angle between the right side or the leftside of the robot and the wall surface is between about 5 degrees andabout 10 degrees.
 5. The robot of claim 1, further comprising a movablebumper defining a portion of the right side and a portion of the leftside of the robot, the bumper configured to contact the wall surface andbe in a partially compressed position in the range when the controlleradvances the robot along the wall surface in the wall followingbehavior.
 6. The robot of claim 5, further comprising a sensorcomprising a first portion mounted to the bumper and a second portionmounted to a body of the robot on which the bumper is mounted, thesensor being configured to produce a signal indicative of the non-zeroangle between the right side or the left side of the robot and the wallsurface.
 7. The robot of claim 5, wherein the bumper is configured to berotated relative to a body of the robot on which the bumper is mountedwhile the controller advances the robot along the wall surface in thewall following behavior.
 8. The robot of claim 1, wherein configurationsof the controller to advance the robot along the wall surface whilemaintaining the non-zero angle between the right side or the left sideof the robot and the wall surface comprises configurations to maintain anon-zero angle between a forward drive direction of the robot and thewall surface.
 9. The robot of claim 1, further comprising a sensorconfigured to produce a signal indicative of the non-zero angle betweenthe right side or the left side of the robot and the wall surface, thesensor selected from the group consisting of a capacitive sensor, a HallEffect sensor, and an inductive sensor.
 10. The robot of claim 9,wherein the sensor is located adjacent to the right side of the robot orthe left side of the robot.
 11. The robot of claim 1, further comprisinga detector associated with a wheel of the robot, the detector beingconfigured to detect a speed of the wheel, wherein configurations of thecontroller to advance the robot along the wall surface compriseconfigurations to adjust a translational speed of the robot based on thedetected speed of the wheel.
 12. The robot of claim 1, wherein thecontroller is configured to control the robot to perform an areacoverage behavior to cover an interior region of a room within an outerperimeter of the room, and configurations of the controller to advancethe robot along the wall surface in the wall following behavior compriseconfigurations to advance the robot along the outer perimeter of theroom after the area coverage behavior is performed.
 13. The robot ofclaim 12, wherein the controller is configured to navigate the robot toan untraversed portion of the interior region of the room afteradvancing the robot along the outer perimeter of the room.
 14. A methodof controlling a mobile cleaning robot, comprising: advancing the robot,in a wall following behavior, along a wall surface; and maintainingcontact between a portion of a cleaning pad of the robot and the wallsurface while advancing the robot along the wall surface in the wallfollowing behavior, while maintaining a position of a bumper of therobot within a range between a fully uncompressed position and a fullycompressed position, and while maintaining a non-zero angle between therobot and the wall surface.
 15. The method of claim 14, whereinmaintaining contact between the portion of the cleaning pad and the wallsurface comprises adjusting rotational and translational speeds of therobot to maintain the contact between the portion of the cleaning padand the wall surface.
 16. The method of claim 14, wherein the non-zeroangle between the robot and the wall surface is between about 1 degreeand about 20 degrees.
 17. The method of claim 14, wherein the non-zeroangle between the robot and the wall surface is between about 5 degreesand about 10 degrees.
 18. The method of claim 14, wherein maintaining anon-zero angle between the robot and the wall surface comprisesmaintaining a movable bumper of the robot in a partially compressedposition in the range while advancing the robot along the wall surfacein the wall following behavior.
 19. The method of claim 14, whereinmaintaining the non-zero angle between the robot and the wall surfacecomprises maintaining a non-zero angle between a forward drive directionof the robot and the wall surface.
 20. The method of claim 14, whereinmaintaining the non-zero angle between the robot and the wall surfacecomprises adjusting a translational speed of the robot based ondetecting a speed of a wheel of the robot.
 21. The method of claim 14,further comprising: navigating the robot along a portion of an interiorregion of a room within an outer perimeter of the room before advancingthe robot along the wall surface in the wall following behavior, andnavigating the robot to an untraversed portion of the interior region ofthe room after advancing the robot along the wall surface in the wallfollowing behavior.